Magnetic Behaviour of the Dihydrate Formates M(HCOO)2 2 H20 of the Transition Metals M Mn, Fe, Co, Ni

Magnetic structures of the dihydrate formates of the transition metals (Mn, Fe, Co, Ni) are reported which are determined by means of neutron diffraction experiments. The magnetic moment directions are interpreted in terms of crystal field anisotropy. In order to determine the influence of anisotropy on the magnetic ordering some mixed compounds of manganese and iron formates are examined. For all these salts the metallic A ions (000, 01‐21‐2) linked together by formic groups show, below TN, a canted antiferromagnetic ordering. The metallic B ions (‐1‐2‐ 0, −1‐2− 0 ‐1‐2‐) not linked together show an ordered moment atlow temperature with respect to TN. In the manganeseand nickel formates the observed directions of the magnetic moments are notrelated to the axis of the oxygen octahedron and are due to a competition between the dipolar anisotropy and a weak single ion anisotropy. In the cobalt and iron counterparts the crystal field effects are strongly dominant and responsible for the observed moment arrangement. In iron formate the Fe2+ ions behave like a pure Ising model. The magnetic behaviour of the Mn formate is strongly affected by iron impurities. For iron concentrations higher than 0.1 the properties of the solid solutions are those of the pure iron salt since in the range of iron concentration 0 < x< 0.1 the solid solutions show a complex behaviour which can be interpreted by a variation of exchange and anisotropy energies.